Traditional microcomposites are comprised of micron-scale particles in an otherwise homogeneous bulk material matrix. Because of their size, such particles generally provide relatively small surface areas compared with their volume, which limits the extent to which the particle can take advantage of interfacial interactions with the matrix in which it is embedded, and, in some cases, tends to impede the uniform distribution of the particles throughout the bulk material. Decreasing the size of the particles used in such composites to nano-scale can result in the formation of composites (“nanocomposites”) in which the nano-scale particles exhibit an enhanced ability to interact with the bulk material and to disperse more uniformly within (or over the surface of) the material.
As such particles become smaller, the ratio of surface area to volume increases, which means any effects or properties associated with the surface of such particles tend to become more dominant. When such nano-scale particles are well dispersed within a bulk material, the effects or properties broadly associated with the interface between the particles and the bulk material—including any functional groups that populate or are chemically attached to the particle surface—may significantly modify the characteristics associated with that bulk material to an extent not usually encountered with micron-scale particles. Processes for achieving the effective dispersion of such particles can include melt-blending (e.g., with an extruder), solvent blending, in-situ polymerization, or solid phase blending such as milling or pulverization such as taught in U.S. Pat. No. 6,180,685 to Khait, et al., the teachings of which are hereby incorporated by reference.
Agglomerations of nanoparticles typically are characterized by having pre-existing surface areas, i.e., those exposed surfaces that are associated with the external topology of the agglomeration, and the potential for having newly or freshly exposed surface areas, i.e., those surfaces that become exposed as a result of the mechanical break-up or rearrangement of the agglomeration, as, for example, occurs in accordance with the ultra-high shear fluidic processing described herein.
The teachings herein are directed in part to the formation of nanoparticle dispersions in a selected solvent wherein at least some of the agglomerations of nanoparticles have been structurally modified (e.g., changed in size, shape, or surface topography), and thereby have been given newly or freshly exposed surface areas onto which functional groups have been placed. Optionally, such nanoparticle/solvent dispersions or the nanoparticles obtained from such dispersions can be incorporated into bulk materials to form nanoparticle/bulk material dispersions in which the properties associated with the functionalized nanoparticles are effectively imparted to the bulk material, either throughout the material or in localized areas such as along a surface or boundary of the material.
If multi-functional nanoparticles are created and introduced within an appropriate heterogeneous composite, and each of the functional groups contributing to the multi-functionality of the particles are respectively compatible with only one or the other of the two dissimilar materials comprising the heterogeneous composite, then the particles typically will tend to concentrate or align themselves along the interface between the dissimilar materials, with particle orientation being largely dictated by the compatibility of the individual functional group with the constituent bulk material with which it is in contact. In such cases, this alignment can be facilitated where the various functional groups populating the nanoparticles surface are segregated or concentrated on specific areas or sides of the nanoparticles.
Such segregation, even if relative or partial, can facilitate the relative physical orientation of the particle with respect to the interface and, by implication, the degree to which the functionality associated with the functional groups on the particle is expressed or observed. This effect can be advantageous in many situations, e.g., where the functionality contributes desirable adhesion or bonding between the two dissimilar materials forming the interface, or where the interaction between the two dissimilar materials is to be impeded or otherwise controlled.
In the discussion that follows, it shall be assumed that the bulk material used is polymeric in nature. It should be understood that other, non-polymeric bulk materials such as suitable organic liquids may also be used in connection with the teachings herein (thus giving rise to interfaces that are solid/liquid or liquid/liquid in nature), with appropriate modifications with respect to dispersion techniques and functional groups that would be apparent to those skilled in the art.